3种星虫线粒体16S rRNA、COI和Cyt b基因片段的序列比较

对裸体方格星虫(Sipunculus nudus)、可口革囊星虫(Phascolosoma esculenta)和澳洲管体星虫(Siphonosoma australe)的线粒体16S rRNA、COI和细胞色素b(Cytb)基因片段序列进行比较,并对其系统发生进行了初步探讨。采用PCR方法得到总长度分别为531～544bp(16S)、652～675bp(COI)和406～453bp(Cytb)的线粒体片段。片段碱基A+T比例较高(16S rRNA基因58.3%,COI基因56.9%,Cytb基因59.5%)。16S rRNA片段存在169个碱基变异位点(其中包括167个简约信息位点)和44个碱基插入/缺失,种内个体间变异较小;COI片段有512个碱基(333个简约信息位点)存在变异,79个碱基插入/缺失;Cytb片段存在347个碱基(318个简约信息位点)变异位点,16个碱基插入/缺失。数据分析结果支持3种星虫和环节动物的分类地位较近,与软体动物较远的分类观点。此外,裸体方格星虫与澳洲管体星虫之间亲缘关系较近(D=0.3159、0.3156、0.2361)。认为3种星虫线粒体16S rRNA、COI和Cytb基因在种间存在明显的多态性,证实了三种基因序列均普遍适用于星虫种及以上阶元的系统学分析。

Sequence Comparison and Phylogenetic Analysis of mtDNA 16SrRNA and CO I and Cyt b Gene Fragments in Three Species of Sipuncula

Sequence comparison and phylogenetic analysis of mtDNA 16SrRNA, CO I and Cyt b gene fragments in three species of Sipuncula were made using PCR and direct squencing. The three species areSipunculus nudus, Phascolosoma esculenta, Siphonosoma australe. Nucleotide sequences of 531-544 bp for 16S rRNA gene,652-675 bp for CO I gene and 406-453 bp for Cyt b were obtained, respectively. A high percentage of A+T base composition in the three sequence was observed. Alignment indicated that variation level of intra-species was low in 16S rRNA sequence. Forty-four indels and 169 variable sites were detected for 16S rRNA gene fragment (of which 167 were parsimony informative ones) across the three species. Three hundred and seventy-nine polymorphic sites were detected in CO I gene fragments and 327 were parsimony informative among the three species, with 18 indels. Three hundred sixty-four polymorphic sites were detected in Cyt b gene fragment and 314 were parsimony informative among the three species, with 14 indels. These genetic distances revealed that the relationship between S. nudus and S. australe was closer than that of Sipunculidae and P. esculenta. Furthermore, the classify status between Sipuncula and Annelida was close than that of Sipuncula and mollusc.